It's playing the odds, but serial killer (search) profiles tend to target white, 20- to 30-something males who are loners and just can't get it right with women.

But sometimes the profile couldn't be farther from the truth. That seemed the case with Derrick Todd Lee (search), the 34-year-old black man with a Casanova reputation recently arrested in connection with a string of murders in Louisiana.

It also was the case last fall in Washington, D.C., where police investigating the Beltway Sniper (search) shootings were looking for a white shooter in a white van and wound up arresting a 41-year-old black man, John Allen Muhammad, and a 17-year-old black youth, Lee Boyd Malvo, both of whom were found sleeping in a blue car.

Experts say profiles are an art, not a science, and although critics say they're too often off the mark, they often are a valuable law enforcement tool.

"Certain people are blaming other people for the profile being wrong rather than getting to the fact that the way the FBI does it is not a science -- it's more guesswork and brainstorming," said investigative psychologist Maurice Godwin.

In the Louisiana case, FBI profilers thought the suspect was likely white -- later said to be Hispanic or light-skinned black -- was a moving target, potentially awkward around women and physically strong. Lee is black, charming and attractive to women.

"This guy should have been behind bars a long time ago, and the police let us down a long time ago," Louisiana resident Geri Teasley told The Associated Press.

But some profile characteristics did match, and experts stress profiles are simply one weapon in law enforcement's arsenal used to track repeat killers.

"A profile's not magical, it's not definitive," said James Alan Fox, criminal justice professor at Northeastern University. "It doesn't necessarily mean it's the key to solving the case."

"The killer is often brought to justice, not because of an accurate profile, not even because of the work of a multimillion-dollar task force," agreed Jack Levin, director of the Brudnick Center on Violence at Northeastern. "Usually, the serial killer makes a mistake -- it's a stroke of luck on the part of investigators."

For example, David Berkowitz, or "Son of Sam," eluded New York police for over a year while he killed six people, until he parked his white Ford Galaxie next to a fire hydrant and got a parking ticket.

Serial killers also get caught when they're cocky. Lee reportedly began talking about his crimes after he got away with them for several months, and maybe even bragged about them.

"When he started opening his mouth, he shut the door on his prison cell," Levin said.

Profiles are based on past killer statistics, who the victims were and/or descriptions extrapolated from crime scene observations, such as how neat it was, whether the body was disposed of and whether it seemed the killer was in a hurry.

"The process of profiling is basically some deductive reasoning based on what you find at a crime scene," Fox said. "It's not of a specificity that will allow you to put out an all-points bulletin."

If the victims were predominantly white, authorities assume the killer is too, since most homicides are same-race. About 70 percent of all serial killers are white and 95 percent are males. This method was used in both cases.

Godwin said Louisiana investigators' biggest mistake was falling victim to "linkage blindness," when law enforcement doesn't share case information across different jurisdictions, so similar murders in surrounding areas aren't factored in.

Godwin said geographic profiles -- based on where the victims were killed -- should be used more frequently and more experts should be brought in.

"There should not be a monopoly by the FBI as consultants to the task force," Godwin said.

Experts agree that public information shouldn't -- and isn't always -- used to develop a suspect profile. It was citizen information that sent Washington-area cops on a wild goose chase looking for a white van.

Another issue is whether these profiles should be released to the media if they're not foolproof.

"I think it's always a great idea for journalists to ask police, 'How do you know what you know? How will you be sure you're not so focused on this that you will miss other obvious clues?'" said Al Tompkins, who teaches broadcast and online journalism at The Poynter Institute.

"I think we all have an obligation to qualify these things," Tompkins added.

But experts agree profiles can be valuable in nailing killers once they're in custody -- but not to track them down.

"It's not like a fingerprint or DNA," Levin said. "It's not a positive means of identification so it can't be used to totally rule out anyone."

"It's just not like on television where they say, 'Here's a profile, go get the guy,'" agreed Fox. "It just doesn't happen."